The present invention generally concerns an improved differential drive, and more particularly relates to a positive traction differential unit differentially transferring rotational forces from a central housing to drivable shafts extending from either side thereof. The present invention is particularly adapted for performance at relative high speed operation, and is reversible.
Differential transmission units, generally for allowing a common rotational input to be differentially transferred between two axle shafts, have long been in existence. For example, in one type of differential transmission unit such as sometimes used in a rear wheel drive automobile, when either of the rear driving wheels begin to slip due to loss of traction, driving input from the automobile drive shaft is diverted to that wheel. Effective drive power for moving the vehicle is thus in proportion to the traction of such slipping wheel. In some instances, power delivered from the drive shaft to the non-spinning wheel is insufficient to move the vehicle, because substantially all of the driving power is being diverted to the slipping wheel. Thus, the vehicle may become immobilized due to the lack of traction of the spinning wheel. Even though the non-slipping wheel may have sufficient traction, it never receives sufficient rotational input for mobilizing the vehicle.
Some prior differential units are generally shown by the following U.S. Pat. Nos. 3,130,604 by Johnson et al.; 2,841,036, by Decker; 1,282,614, by Miller; 1,238,659, by Ford; and 1,162,754, by Deegan.
Some other types of differential transmission units may be locked, either manually or automatically, for transmitting rotational drive power from a drive shaft to a pair of drive axles so that wheels mounted thereon deliver driving torque to a road surface, even if one of the wheels tends to slip or spin. Such differential transmission units are commonly referred to as limited slip or positive traction differential units. Such locking may be variously accomplished. For example, U.S. Pat. No. 2,967,438, granted to Altmann, and U.S. Pat. No. 2,938,407, granted to Nallinger et al., each generally prevent a slipping wheel from receiving all of the driving input from a drive shaft, by variously diverting some power from the driving shaft to the axle connected to the other, i.e., non-slipping, wheel. The Altmann and Nallinger units generally use ball-like members which selectively engage different members during operation.
U.S. Pat. No. 1,823,092 granted to De Lavaud relates to a differential unit with unitary rollers carried by two respective hubs. The rollers extend into grooves in a surrounding sleeve. As such sleeve rotates, portions of the grooves are brought into contact with the unitary rollers which, in turn, frictionally engage their respective hub to turn an output shaft uniquely associated therewith. During a vehicle turn, an "outer" wheel normally rotates faster than an "inner", positively engaged wheel. The hub corresponding to such outer wheel rotates a limited amount relative to the still-engaged hub, which brings such roller to a central, intermediate area of the groove, thereby releasing any frictional engagement between the free-wheeling output shaft and the surrounding sleeve. Numerous parts, subject to large, changing forces, are needed for allowing such relative rotation between the respective hubs on which the unitary rollers are independently carried, all of which is required to achieve the De Lavaud differential action.